Abnormalities of cellular or tissue heterogeneity are thought to provide a mechanism for many forms of human arrhythmias. The objective of this project is to develop technologies that will correlate the structural and functional relationships of cardiac tissue morphology and conduction heterogeneities. This project will provide an enhancement to viewing the conduction of action potentials within cardiac tissue in three dimensions. By coupling functional imaging with structural imaging, three dimensional structural imaging and depth information of the action potentials can be acquired simultaneously. With this new system, we can test the hypothesis if there is a structural basis for the heterogeneity of action potential velocities and morphology in the AV node. Isolated AV node preparations from New Zealand White Rabbits will be used as a model in this project. Other models of cellular or tissue heterogeneity can be imaged with this system to correlate the structure-function relationship in substrates of arrhythmias.